Proposed Canon

It is worn on the forearm, covering the upper part from elbow to wrist. Two straps hold it to the arm. The upper portion is similar to hard plastic and includes a spot where Parson's calculator watch can snap in.[2] The watch is vital to its function: without the watch, the bracer does nothing.

The bracer instantly and effortlessly does raw calculations necessary to analyze probabilities and predict outcomes of battles - that is, Mathamancy.[3] It also seems to use Predictamancy and Date-a-mancy to gather some of the variables needed for these calculations. Casters with an appropriate discipline can channel juice with it to aid their own abilities. For example, Benjamin, a Moneymancer, is able to use it to manage Transylvito's finances far more efficiently. It's ability to calculate probabilities go far beyond what a normal Mathamancer is capable of, to the point of being able to accurately predict someone's decisions.

It can be operated by voice command or subvocalizations, similar to the eyebooks.[4]

Variable Detection

The Bracer can automatically acquire certain variables needed for its calculations, including information users themselves do not possess. Known variables it can detect are:

Total treasury of the user's side, though attempting to learn the value of a different side's treasury results in UNKNOWN or ERROR.

Whether or not and what kind of magic a member of the user's side has had cast on them.

Your current level. It can even detect Parson's level, which is invisible to other units.[5]

Whether or not a unit on the user's side is wearing a given item.

Whether or not a given unit is acting as an agent of a given side.

Whether or not a given side has received financial support from another side, though it cannot detect the amount.

Calculations for Charlie

Towards the end of the Battle for Gobwin Knob, Parson made a magically-binding deal with Charlie; twelve Mathamancy battle evaluations in exchange for not aiding Transylvito in ambushing Stanley.[6] As a formal contract, Charlie had the ability to force Parson to make the calculations at any time.

Calculations Spent:

Two calculations on the strength of Gobwin Knob vs. hypothetical Archon attacks. These calculations were requested immediately after the deal was made.[7]

One calculation on the odds of Gobwin Knob still standing after at the end of the current turn.[8]

One calculation on the odds that forfeiting the eight remaining calculations would be a fair exchange for learning why the Archon units lost at Gobwin Knob now fight for Stanley. The calculation (a 4.14% chance of the exchange being worth it) led Charlie to refuse the deal. This calculation backfired: it taught Parson how to use his bracer to perform sophisticated calculations (and meta-calculations) on abstract future events.[9]

One calculation on the odds that Parson is capable of casting the scrollJojo gave him.[10] In this case, the bracer gave glitched results. An unidentified force tampered with the bracer, giving a chance of zero. However, Parson noted that the bracer briefly showed a different result. By asking the bracer to perform the calculations ten times in a row, Parson was able to see both results--0 and .980104773. Parson then blamed the conflicting results as being "railroaded by two different GMs".

Shortly after the Siege of Spacerock, Charlie forfeited the rights to the remaining six calculations in exchange for sparing Jillian of Faq, among other concessions.[12]

Speculation

Sizemore Rockwell hypothesized that it may be an Artifact. A broad estimate of the value is around 500,000 Shmuckers to the right buyer (a Side reliant on Mathamancy), the very value of the Summoning Spell including the casting and support package. Given that the Spell that created the Bracer was created by the residents of the Magic Kingdom, whether the Bracer qualifies by the strict letter of the definition of Artifact depends on the inner workings of the spell itself, something which we have not yet been made privy.

The effects of the bracer, when combined with Parson's calculator watch, effectively turns its user into a Mathamancer.

Predictions about future

The bracer seems capable of making sophisticated predictions about the future (as seen on LIAB Prologue 18), so the bracer may have rudimentary Predictamancy abilities as well. (Or it is just really, really powerful Mathamancy.) It is also notable that it was able to detect that Fate would prevent Parson from being able to cast the Dismiss Perfect Warlord spell.

This is less predictamancy (foretelling a specific future event) and more extremely advanced mathamancy in the vein of oddsmaking/handicapping, though it certainly manages to calculate influences seemingly out of the mortal purview.

Another thing to note is that it can predict one's decisions and determine Parson's level, which would imply that it has power in Date-a-mancy.

This definitely pushes the Bracer into Artifact category. It is essentially a Do-It-Yourself-instant-Mathamancer/Predictamancer. I don't think mere mortals have the power to do something like that. (At least as cost-effectively.)